If you're into iPod hacks and you've got a 5G video iPod, you can create and enable a screensaver on your iPod in a few simple steps. Here's how:

Create a new folder named Demo Mode on the iPod.

In iTunes, rename any video file as Demo

Don't play anything and keep the iPod on a charger. In 2 minutes the video you renamed as Demo will automatically play and repeat.

The screensaver (unfortunately) works only when your iPod isn't playing and is charging, but it is a neat Easter egg that I'd never seen. However, if you really want to supercharge your iPod, you should give iPodLinux a try. — Adam Pash